Over-current/over-temperature protection device

ABSTRACT

An over-current/over-temperature protection device (1) which includes first and second electrical contacts (2,3), a separable resistance electrical current path (4) extending between the contacts, a breaker (6) and a heater. The heater comprises the separable path (4). The breaker breaks an electrical connection between at least one of the contacts and the separable path when current above a threshold value passes through the separable path and/or the over-current/over-temperature protection device reaches a threshold temperature. The breaker (6) includes a member of a shape memory alloy which changes shape from a first configuration to a second configuration when the member is heated from a first temperature T 1  to a second temperature T 2 . The heater heats the member from the first temperature T 1  to the second temperature T 2  so that the member changes from the first configuration to the second configuration. The device can optionally include a permanent resistance electrical current path (5) having a resistance higher than the separable path (4). The device can also include a button (110) for resetting the device or a control circuit for remotely completing or breaking the electrical connection between the separable path and the contacts.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.07/687,792 filed Apr. 19, 1991, now U.S. Pat. No. 5,105,178.

FIELD OF THE INVENTION

This invention relates to circuit protection devices that limit or shutoff current flow in conditions of over-current and/or over-temperature.

DESCRIPTION OF RELATED TECHNOLOGY

Raychem Corporation, Menlo Park, Calif. markets a circuit protectiondevice called a "polyswitch." Raychem's "polyswitch" includes apolymeric material loaded with conductive material, such as carbonparticles, which is normally conductive. If the current load increasesbeyond a predetermined value, the polymer heats up and expands with theresult that the conductive particles are separated enough to preventflow of current through the polymer. A problem with this polymeric typedevice is that it has an undesirable slow response time due to lowthermal conductivity of the polymeric materials. Accordingly, there is aneed in the art for a device which quickly changes from a low resistanceto a high resistance when an over-current or an over-temperaturecondition exists.

Another problem with the polymeric device is internal "arcing" whichoccurs when the current flow is interrupted between adjacent particles.This internal "arcing" leads to breakdown of the polymer and hencelimits the upper voltage which can be applied to the device.Accordingly, there is a need in the art for a more reliable switchcapable of performing under higher voltage and current conditions.

Another inherent problem of polymeric devices is that the conductivityis relatively low, even in its most conductive state. As a result, highcurrent devices are undesirably large in size when low resistance levelsare required.

Ceramic PTC (positive temperature coefficient) devices based on bariumtitanate perform very similarly to polymeric devices and also displaycatastrophic breakdown when exposed to elevated voltage and/or currentconditions.

Various types of mechanical switching arrangements are known in the art.For instance, U.S. Pat. No. 3,544,943 ("Hoagland") discloses anover-current responsive device which includes a pair of terminalselectrically connected together by a thermally responsive element. Thethermally responsive element includes two elongated cantilevered memberssupported at one end to a pair of posts. The posts are electricallyconnected to the terminals. The first elongated member is electricallyinsulated from the posts. One end of the second elongated member iswelded to a free end of the first member. The second member is alsobifurcated into two arms, one arm being electrically connected to onepost and the other arm being electrically connected to the other post.Current flows from one terminal, along one arm, then along the other armto the other terminal. The size, shape, and/or materials of the firstand second members are chosen such that the second member is heated andthe two members swing in one direction to activate a snap-action switchunder overload conditions.

Shape memory alloys have been used in electrical connectors. Forinstance, U.S. Pat. No. 4,621,882 ("Krumme '882") discloses anelectrical connector wherein a first strip which terminates in a splittube is removably connected to a second strip. The split tube includes ashape memory alloy layer which opens or closes the tube. For instance,the tube can include a metal layer which acts as a spring to close thetube when the shape memory layer is in its ductile and soft martensiticstate, and the shape memory layer changes shape and overpowers the forceof the metal layer when the shape memory layer is heated to itsaustenitic state. The tube can include a flexible heater for heating theshape memory layer.

U.S. Pat. No. 4,643,500 ("Krumme '500") discloses a multi-contact zeroinsertion force electrical connector. In a first embodiment, theconnector includes a pair of flexible spaced-apart sidewalls, slideshaving camming surfaces extend along inner surfaces of the sidewalls,pairs of spaced-apart contacts are provided between the sidewalls, upperends of the contacts are attached to the respective sidewalls byextensions on the sidewalls, and the slides are pushed and pulled bymeans of a shape memory U-shaped Nitinol (nickel-titanium) wire whichextends around the sidewalls with free ends of the wire connected toterminals. To insert a printed circuit board between the sidewalls,current is applied across the terminals to heat the wire to itsaustenitic state which causes the wire to shrink to a memory state. As aresult, the upper portions of the sidewalls are pushed apart by theslides. Upon cooling of the wire, the sidewalls move toward each otherand the contacts clamp the circuit board in place.

In another embodiment, Krumme '500 discloses opposed pairs of contactssupported in a body, a U-shaped bail is slidably supported between thecontacts, an S-shaped Nitinol member is between the body and the bail,and a pair of leads is connected to the Nitinol member for heatingthereof or heating a heater bonded thereto. When the Nitinol member isheated to its austenitic state it expands and pushes up on the bailwhich in turn pushes the contacts apart. The Nitinol member can becovered with insulation to prevent electrical contact with the contacts.

U.S. Pat. No. 4,734,047 ("Krumme '047") discloses a multi-contact zeroinsertion force electrical connector. In a heat-to-open embodiment, aplurality of fork-shaped contacts includes distal ends for holding asubstrate. A split tube of a shape memory alloy is provided between thedistal ends for spreading the distal ends when the alloy is heated toits austenitic state. A spring is concentrically layered with respect tothe tube for deforming the tube when the alloy is in its martensiticstate. The alloy is heated by a heater located within the tube.Alternatively, in a cool-to-open embodiment, the spring can be providedwithin the tube, and the contacts are opened by cooling the alloy to itsmartensitic state whereby the spring expands the tube to spread thedistal ends. The spring can be eliminated in the heat-to-open embodimentsince the contacts are resilient and will deform the tube when the alloyis in its martensitic state. In addition, the tube can be resistanceheated by passing a current therethrough.

U.S. Pat. No. 4,881,908 ("Perry") discloses a connector having a springin the form of an elongated split tube and a heat-recoverable member ofshape memory alloy positioned within the tube. Opposed sets of contactpads are positioned between the ends of the spring and are movable intoand out of contact with a substrate inserted between the contact pads.To open the connector, the shape memory alloy is heated by passing acurrent therethrough or by using a resistance heater circuit or aseparate resistance heater. For instance, a heater can be providedbetween the spring and the shape memory alloy. When the shape memoryalloy is in a deformable state below a transition temperature, thespring deforms the shape memory alloy to close the connector. When theshape memory alloy is in a memory state above the transitiontemperature, the shape memory alloy recovers to its non-deformed state.

SUMMARY OF THE INVENTION

The invention provides an over-current and/or over-temperatureprotection device which includes first and second electrical contacts, aseparable electric current path extending between the contacts, breakermeans and heater means. The heater means comprises the separable pathwhich can be a high or low resistance path. The breaker means breaks anelectrical connection between at least one of the contacts and theseparable path when current above a threshold value passes through theseparable path. The breaker means includes a member of a shape memoryalloy which changes shape from a first configuration to a secondconfiguration when the member is heated from a first temperature T₁ to asecond temperature T₂. The heater means heats the member from the firsttemperature T₁ to the second temperature T₂ so that the member changesfrom the first configuration to the second configuration.

According to one aspect of the invention, theover-current/over-temperature protection device can be self-resetting.In this case, the over-current/over-temperature protection deviceincludes means for changing the member into the first configuration whenthe member cools from the second temperature T₂ to a third temperatureT₃ deemed safe for operation of the circuit being protected. The thirdtemperature T₃ is below T₂ and preferably is at least about 15° C. belowT₂.

According to another aspect of the invention, theover-current/over-temperature protection device can include means forminimizing arcing when the electrical connection between the separablepath and at least one of the contacts is broken by the breaker means.The arc minimizing means comprises a permanent electrical current pathextending between the contacts. The permanent path can have a highresistance to flow of electrical current therethrough. The resistance ofthe permanent path can be any value but typically is at least two timesthat of the separable path. Any ratio of resistance is attainablebetween the separable and permanent paths.

The separable and permanent paths can each comprise a flex circuit whichincludes an electrically conductive layer such as a sputtered metallicor non-metallic conductive film or screen printed conductive ink on apolymer film. The separable and permanent paths can each include a layerof dielectric material on the conductive layer. The dielectric materialprevents flow of electrical current from the separable and/or permanentpaths to the member while allowing the member to be heated to the secondtemperature T₂ by heat produced by the conductive layer when currentflows through the separable and/or permanent paths.

In one embodiment, the contacts have free ends located in an interiorspace within a housing. The free ends of the contacts are movable from afirst position in electrical contact with the separable path to a secondposition out of electrical contact with the separable path. The contactsare in the first position when the member is in the first configuration,and the contacts are in the second position when the member is in thesecond configuration. The member can be U-shaped with one free endthereof facing the first contact and another free end thereof facing thesecond contact. The ends of the U-shaped member can be closer togetherin the first configuration than in the second configuration. Thecontacts can be spring loaded such that the contacts return to the firstposition when the member changes from the second configuration to thefirst configuration. The housing can include first, second and thirdsupport surfaces in the interior space. The first support surface can bearcuate and face a central portion of the polymer film of the separablepath. The second and third surfaces can be opposite sides of a wall. Thesecond support surface can be attached to one end of the polymer film,and the third support surface can be attached to an opposite end of thepolymer film. The U-shaped member can be supported between the polymerfilms of the separable and permanent paths.

In another embodiment, the contacts include contact zones which areimmovable with respect to each other. The separable path has free endswhich are movable from a first position in electrical contact with thecontact zones to a second position out of electrical contact with thecontact zones. The free ends of the separable path are in the firstposition when the member is in the first configuration, and the freeends of the separable path are in the second position when the member isin the second configuration.

The member can be U-shaped, and the contact zones can be located betweenfree ends of the U-shaped member. The free ends of the U-shaped membercan be closer together in the first configuration than in the secondconfiguration. A spring can be provided for biasing the free ends of theseparable path in the first position. The spring can comprise a bentstrip having an arcuate central portion and inwardly curved end sectionsextending from the central portion. Each free end of the separable pathcan be attached to a respective end section of the spring. The springbiases the free ends of the separable path toward the contacts so thatthe separable path is in electrical contact with the contact zones whenthe U-shaped member is in its first configuration. The U-shaped memberbends the end sections of the spring outwardly away from the contactzones when the U-shaped member is in the second configuration.

The housing can include first, second and third support surfaces withinthe interior space. The first contact zone can be attached to the firstsupport surface. The second contact zone can be attached to the secondsupport surface. The permanent path can be attached to the third supportsurface. The first and second support surfaces can comprise oppositesides of a wall extending from a base of the housing and into a centerof the interior space. The first contact zone can comprise a conductivelayer on the first support surface, the second contact zone can comprisea conductive layer on the second support surface, and the polymer filmof the permanent path can be adhesively bonded to the third supportsurface. The third support surface can be convex in cross-section andface a concave portion of the U-shaped member. The housing can include apair of leads on an exterior surface thereof, and the leads can beelectrically connected to the contact zones.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described with reference to the attached drawing, inwhich:

FIG. 1 shows a cross-section of a self-resettingover-current/over-temperature protection device in accordance with oneembodiment of the invention;

FIG. 2 shows a side view of a resistance electrical current path usablein the over-current/over-temperature protection device of the invention;

FIG. 3 shows a side view of the resistance path shown in FIG. 2 withcontact pads thereon;

FIG. 4 shows a side view of the resistance path shown in FIG. 3 with adielectric layer and an adhesive layer thereon;

FIG. 5 shows a top view of a ribbon which can be cut to provide aplurality of resistance paths usable in theover-current/over-temperature protection device of the invention;

FIG. 6 shows a self-resetting over-current/over-temperature protectiondevice in accordance with a second embodiment of the invention;

FIG. 7 shows a perspective exploded view of various parts; of thearrangement shown in FIG. 6;

FIG. 8 shows a cross-section of a manually resettableover-current/over-temperature protection device in accordance with athird embodiment of the invention wherein a current path has beenbroken;

FIG. 9 shows a cross-section of the device shown in FIG. 8 wherein thecurrent path has been manually reset;

FIG. 10 shows a cross-section of a remotely resettableover-current/over-temperature protection device in accordance with afourth embodiment of the invention;

FIG. 11 shows a perspective exploded view of various parts of thearrangement shown in FIG. 10;

FIG. 12 shows a side view of a resistance electrical current path usablein the over-current/over-temperature protection device of the invention;

FIG. 13 shows a side view of the resistance path shown in FIG. 12 withcontact pads thereon;

FIG. 14 shows a side view of the resistance path shown in FIG. 13 with adielectric layer and an adhesive layer thereon;

FIG. 15 shows a top view of a ribbon which can be cut to provide aplurality of resistance paths usable in theover-current/over-temperature protection device of the invention;

FIG. 16 shows a top view of the control current path and the contacts ofthe self-resetting over-current/over-temperature protection device inaccordance with a second embodiment of the invention; and

FIG. 17 shows a side view taken along the line 17--17 in FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides an over-current/over-temperature protectiondevice which interrupts flow of electrical current between two contactsin response to either an over-current and/or over-temperature condition.The over-current/over-temperature protection device can be designed tomeet the needs of a wide variety of electrical circuits. In particular,the over-current/over-temperature protection device can be designed torapidly break an electrical connection in response to a current ortemperature overload condition.

The over-current/over-temperature protection device includes first andsecond electrical contacts, a separable electrical current pathextending between the contacts, breaker means and heater means. Theheater means comprises the separable path. The breaker means breaks anelectrical connection between at least one of the contacts and theseparable path when current above a threshold value passes through theseparable path. The breaker means includes a member made of shape memoryalloy such as NiTi which changes shape from a first configuration to asecond configuration when the member is heated from a first temperatureT₁ to a second temperature T₂. The heater means heats the member fromthe first temperature T₁ to the second temperature T₂ so that the memberchanges from the first configuration to the second configuration.

According to one aspect of the invention, theover-current/over-temperature protection device can be self-resetting.In this case, the over-current/over-temperature protection deviceincludes means for changing the member back into the first configurationwhen the member cools from the second temperature T₂ to a thirdtemperature T₃ deemed safe for current operations, typically about 15°C. below T₂.

According to another aspect of the invention, theover-current/over-temperature protection device can include means forminimizing arcing when the electrical connection between the separablepath and at least one of the contacts is broken by the breaker means.The arc minimizing means comprises a permanent electrical current pathextending between the contacts, the permanent path having a highresistance to flow of electrical current therethrough. The resistance ofthe high resistance path can be any value. For instance, the resistanceof the permanent path can be two times or more than that of theseparable path. Virtually any ratio of resistances between the separableand permanent paths can be used depending upon specific circuit needs.

A first embodiment of the over-current/over-temperature protectiondevice of the invention is shown in FIG. 1. Theover-current/over-temperature protection device includes first andsecond electrical contacts, a separable electrical current pathextending between the contacts, breaker means and heater means. Theheater means comprises the separable path. The breaker means breaks anelectrical connection between the separable path and at least one of thecontacts when current above a threshold value passes between thecontacts through the separable path. The breaker means includes a membermade of a shape memory alloy which changes shape from a firstconfiguration to a second configuration when the member is heated from afirst temperature T₁ to a second temperature T₂. The heater means heatsthe member from the first temperature T₁ to the second temperature T₂ sothat the member changes from the first configuration to the secondconfiguration.

The over-current/over-temperature protection device can be madeself-resetting by providing means to reset the contacts and the memberto their original positions. This can be accomplished by making thecontacts from a spring material and biasing them together.Alternatively, the over-current/over-temperature protection device canbe manually resettable by suitable means.

The over-current/over-temperature protection device can also includemeans to minimize arcing when the electrical connection between theseparable path and the contacts is broken. The arc minimizing meanscomprises a permanent resistance electrical current path that remainscontinuous (i.e., unbroken) whether the separable path is or is not inelectrical contact with both of the contacts. The permanent path canalso provide enough heat to the member to maintain it in its secondconfiguration until the over-current and/or over-temperature conditionis relieved or removed.

The over-current/over-temperature protection device shown generally at 1in FIG. 1 includes first and second electrical contacts 2,3. Separableelectrical current path 4 extends between contacts 2,3, and permanentelectrical current path 5 extends between contacts 2,3. Breaker meansshown as member 6 breaks an electrical connection between at least onecontact 2,3 and separable path 4 when current above a threshold valueflows through separable path 4 and/or permanent path 5.

The breaker means comprises member 6 made of a shape memory alloy suchas a strip of Ni--Ti which changes shape from a first bent configurationto a second less bent configuration when member 6 is heated from firsttemperature T₁ to second temperature T₂. Separable path 4 and/orpermanent path 5 perform an additional function of heating member 6 fromfirst temperature T₁ to second temperature T₂ when current above thethreshold value flows through separable path 4 and/or permanent path 5.As a result, member 6 changes shape from the more bent configuration tothe less bent configuration and forces contacts 2,3 to spread apart soas to be out of contact with separable path 4.

Permanent path 5 minimizes arcing when the electrical connection betweencontacts 2,3 and separable path 4 is broken by member 6. That is,permanent path 5 provides an alternative path for flow of electricalcurrent between contacts 2,3. The ratio of the resistance of permanentpath 5 to that of Separable path 4 can be set at any arbitrary valuesuch as 2:1, 50:1, 100:1, 250:1, 500:1, 1000:1, etc. For instance, theresistance of separable path 4 could be 1 ohm, and the resistance ofpermanent path 5 could be 100 ohms or higher. In addition to minimizingarcing, permanent path 5 continues to provide an adequate heating effectto maintain the device in its "open" or "tripped" condition until theover-current and/or over-temperature condition causing triggering of thedevice is relieved or removed.

To manufacture separable path 4, electrically conductive layer 7 isdeposited on polymer film 9, as shown in FIG. 2. Likewise, permanentpath 5 can be manufactured by depositing electrically conductive layer 8on polymer film 10. Conductive layer 8, however, preferably has a higherelectrical resistance than layer 7. The higher resistance of layer 8 canbe obtained in various ways. For instance, if layers 7,8 comprise thesame material and are deposited in the same thickness, permanent path 5could comprise a more narrow strip of composite 8,10 than composite 7,9.That is, the wider strip comprising separable path 4 can have a greaterarea over which the current flows and thus lower resistance to the flowof current therethrough compared to permanent path 5.

As an example, polymer film 10 can comprise a polyimide film which is0.0005 to 0.001 inch (0.0127 to 0.0254 mm) thick and 0.075 inch (1.905mm) wide. Conductive layer 8 can comprise a nichrome sputtered depositon polymer film 10. The thickness of nichrome layer 8 can be adjusted inaccordance with the desired resistance of the permanent path 5. Forinstance, the thickness of nichrome layer 8 can be adjusted to provide aresistance of 1000 ohms. Separable path 4 can comprise a polyimide film9 which is 0.0005 to 0.001 inch (0.0127 to 0.0254 mm) thick and 0.05inch (1.27 mm) wide with a nichrome or copper layer 7 thereon in athickness to provide a desired resistance such as 1 ohm. Accordingly,various materials and dimensions (length, width, thickness) can beutilized in designing separable and permanent paths 4,5.

Separable and permanent paths 4,5 can be used with or without one ormore electrically insulating coatings. However, to prevent leakage ofcurrent to surrounding electrically conducting materials, paths 4,5 canbe provided with a coating of dielectric material. For instance,separable path 4 can include layer 11 of dielectric material onconductive layer 7, as shown in FIG. 4. Likewise, permanent path 5 caninclude layer 12 of dielectric material on conductive layer 8. Thedielectric material can comprise any suitable electrically insulatingmaterial such as polymer or ceramic materials.

The dielectric material 11,12 can be applied in any suitable manner suchas by techniques conventionally used in semiconductor processing. Forexample, a sheet of polymer film 9,10 of polyimide having a metalliclayer of nichrome 7,8 can be masked off, and dielectric layer 11,12 canbe deposited on the nichrome layer 7,8 in a desirable pattern. Thearticle shown in FIG. 5 comprises a ribbon cut from such a sheet ofpolyimide 9,10 having nichrome layer 7,8 and dielectric layer 11,12thereon. Separable paths 4 can comprise strips cut from the ribbon shownin FIG. 5. Likewise, permanent paths 5 can comprise more narrow stripscut from the same or a similar ribbon.

Separable and permanent paths 4,5 can be used with or without contactpads. However, to provide for optimized current flow into and out ofpaths 4,5, pads 13 of an electrically conducting corrosion resistantmaterial can be provided on conductive layers 7,8. For instance, pads 13can comprise a layered structure of copper, nickel, gold, etc. Or, forinstance, pads 13 could comprise a single layer of copper with tin-leadsolder plating over the copper layer.

To form pads 13, the metal or metals of the pad can be plated onconductive layers 7,8. For instance, if dielectric layer 11,12 isalready present, the metal or metals of pads 13 can be plated directlyon conductive layers 7,8.

As shown in FIG. 1, member 6 is surrounded on both sides by paths 4,5.Dielectric layer 11 on separable path 4 faces and/or contacts member 6and prevents flow of electrical current from separable path 4 to member6 while allowing member 6 to be heated to second temperature T₂ by heatproduced by conductive layer 7 when current above a threshold valueI_(c) flows through separable path 4. Dielectric layer 12 can be incontact with member 6 to prevent flow of electrical current frompermanent path 5 to member 6. Paths 4,5 can be used with or withoutadhesive means thereon. However, to provide for attachment to otherparts, paths 4,5 can include adhesive layers 14,15. For instance,polymer film 9 can include adhesive layer 14 on one side and conductivelayer 7 on the other side thereof, as shown in FIG. 4. Likewise, polymerfilm 10 can include adhesive layer 15 on one side and conductive layer 8on the other side thereof. Additional adhesive layers could be providedon dielectric layers 11,12, if desired.

In the embodiment shown in FIG. 1, housing 16 includes interior space 17within which contacts 2,3, paths 4,5 and member 6 are located. Housing16 can be extremely small in size with an overall height of about 0.5inch (12.7 mm) and a width of less than 0.5 inch (12.7 mm), for example.Of course, the principles of the invention can be applied to larger orsmaller devices.

Contacts 2,3 have free ends 18,19 thereof within interior space 17. Freeends 18,19 are movable from a first position in electrical contact withseparable path 4 (as shown in FIG. 1) to a second position (not shown)out of electrical contact with separable path 4. Free ends 18,19 are inthe first position when member 6 is in its first configuration, and freeends 18,19 are in the second position when member 6 is in its secondconfiguration.

Member 6 can be U-shaped in the first and second configurations with onefree end 20 facing first contact 2 and another free end 21 facing secondcontact 3. Free ends 20,21 are closer together when member 6 is in itsfirst configuration than when member 6 is in its second configuration.Member 6 can comprise a rectilinearly extending strip which is bent intoa U-shape in its easily deformed martensitic condition at firsttemperature T₁. When heated to second temperature T₂, member 6 changesinto its austenitic state and attempts to revert to its memorized flatcondition thereby causing free ends 20,21 to spread apart and force freeends 18,19 of contacts 2,3 away from each other.

Contacts 2,3 can be of an elastic or springy material such asberyllium-copper (Be--Cu). In the arrangement shown in FIG. 1, contacts2,3 include U-shaped bends which are received in corresponding U-shapedgrooves in housing 16. This arrangement holds contacts 2,3 in a preciserelationship to each other and such that they are spring loaded. Springloaded contacts 2,3 return to the first position when member 6 changesfrom the second configuration to the first configuration. As explainedearlier, member 6 is easily deformed at the first temperature T₂ sinceit is in its martensitic condition. As such, spring loaded contacts 2,3bend member 6 into its first configuration when member 6 cools fromsecond temperature T₂ to a lower temperature T₃ such as about 15° C.lower than T₂. Alternatively, contacts 2,3 can be spring loaded so as tobe biased toward each other by other suitable means such as a spring(s),elastomeric material, or other mechanical equivalent.

As shown in FIG. 1, housing 16 can include arcuate support surface 22 ininterior space 17. Central portion 23 of separable path 4 extends aroundsurface 22. Surface 22 can face polymer film 9 of separable path 4. Tosecure separable path 4 in position, adhesive layer 14 can be used toattach polymer film 9 to surface 22.

Housing 16 can include support surfaces 24,25 to which opposite ends ofseparable path 4 are attached. In the arrangement shown in FIG. 1,surfaces 24,25 are spaced apart and face in opposite directions. One endof separable path 4 can be attached to surface 24 by means of adhesivelayer 14, and the opposite end of separable path 4 can be attached tosurface 25 by adhesive layer 14.

A second embodiment of the invention is shown in FIGS. 6-7. In thisembodiment, over-current/over-temperature protection device 1b includescontacts 52,53 which have contact zones located in interior space 60within a housing. Contacts 52,53 are immovable with respect to eachother, and permanent path 55 provides a non-separable high resistanceelectrical path between contacts 52 and 53. Separable resistance currentpath 54 has contact zones 91,92 which are movable from a first position(as shown in FIG. 6) in electrical contact with contact zones ofcontacts 52,53 to a second position out of electrical contact therewith.Contact zones 91,92 are in the first position when member 56 is in afirst configuration (as shown in FIG. 6), and contact zones 91,92 are inthe second position when member 56 is in a second configuration.Separable path 54 preferably has a lower resistance than permanent path55.

Spring 57 is provided for biasing the contact zones 91,92 of separablepath 54 in the first position. Spring 57 comprises an elastic striphaving an arcuate central portion and ring-shaped end sections extendinginwardly from the central portion. Contact zones 91,92 of separable path54 are attached to the respective end sections of spring 57. Spring 57biases contact zones 91,92 of separable path 54 toward the contact zonesof contacts 52,53 so that separable path 54 is in electrical contactwith contacts 52,53 when the U-shaped member 56 is in its firstconfiguration. U-shaped member 56 bends the end sections of spring 57outwardly away from the contact zones of contacts 52,53 when U-shapedmember 56 is heated from a first temperature T₁ to a second temperatureT₂ to change member 56 into the second configuration.

A housing of the over-current/over-temperature protection deviceincludes base 58 and cover 59. Base 58 includes first, second and thirdsupport surfaces 61-63 within interior space 60. The contact zone offirst contact 52 is attached to first support surface 61. The contactzone of second contact 53 is attached to second support surface 62.Permanent path 55 is attached to third support surface 63. First andsecond support surfaces 61,62 comprise opposite sides of wall 64extending from base 58 and into the center of interior space 60 withincover 59. Surface 63 comprises an outer surface of an enlargementextending from one end of wall 64. First contact 52 can comprise acopper plating, second contact 53 can comprise another copper platingand permanent path 55 can comprise a nichrome film on a single strip ofpolymer film. Alternatively, contacts 52,53 and permanent path 55 cancomprise coterminous metal layers on a polymer film. For instance,contacts 52,53 and permanent path 55 can comprise a polymer film withcoterminous metallic layers on one side thereof. The metallic layers caninclude a metallic layer such as nichrome on a central portion of thepolymer film and metallic layers such as copper on ends of the polymerfilm. In this case, the central metallic layer comprises permanent path55, and the other metallic layers comprise contacts 52,53. The polymerfilm can include adhesive to attach the film to surfaces 61-63.

In cases where the over-current/over-temperature protection device isnot automatically resettable, the over-current/over-temperatureprotection device can include a manually resettable mechanism. Forexample, a movable button extending through an upper part of the housingcan be provided for pushing the spring and shape memory alloy memberback into configurations in which separable path 54 is in contact withthe contact zones of contacts 52,53. In this case, theover-current/over-temperature protection device shown in FIG. 6 caninclude biasing means such as a pair of springs urging the respectiveend sections of spring 57 away from base 58 and toward an upper part ofcover 59. When member 56 is in its first configuration, however, contactzones 91,92 of separable path 54 tightly grip the contact zones ofcontacts 52,53 by friction, thus preventing spring 57 from movingupwardly along wall 64 due to the force of the biasing means. When anover-current/over-temperature condition exits, contact zones 91,92 moveaway from the contact zones of contacts 52,53. As a result, the biasingmeans pushes spring 57 upwardly. Cover 59 can include a suitably shapedrecess for receiving the reset button such that the button extends onlyout of cover 59 when spring 57 is moved upwardly due to anover-current/over-temperature condition. Once theover-current/over-temperature condition no longer exits, member 56 willcool and transform to its martensitic condition thereby allowing spring57 to press against opposite sides of wall 64 when the button isdepressed.

A third embodiment of the over-current/over-temperature protectiondevice of the invention is shown in FIGS. 8 and 9. Theover-current/over-temperature protection device is manually resettableand includes first and second electrical contacts, a separableelectrical current path extending between the contacts, breaker means,heater means and resettable means. The heater means comprises theseparable path. The breaker means breaks an electrical connectionbetween the separable path and at least one of the contacts when currentabove a threshold value passes between the contacts through theseparable path. The breaker means includes a member made of a shapememory alloy which, if unrestrained, changes shape from a firstconfiguration to a second configuration when the member is heated from afirst temperature T₁ to a second temperature T₂. The heater means heatsthe member from the first temperature T₁ to the second temperature T₂ sothat the member undergoes a metallurgical phase change wherein themember attempts to assume a memorized shape.

Manually resettable over-current/over-temperature protection device 100includes housing 102, base 103, and first and second electrical contacts104,105. Separable electrical current path 106 extends between contacts104,105. Breaker means 108 breaks an electrical connection between atleast one contact 104,105 and separable path 106 when current above athreshold value flows through separable path 106.

Breaker means 108 is made of a shape memory alloy such as a strip ofNi--Ti which undergoes a metallurgical phase change which causes thebreaker means 108 to attempt to change shape from a first bentconfiguration to a second less bent configuration when breaker means 108is heated from first temperature T₁ to second temperature T₂. Forinstance, breaker means 108 can be a strip having a memorized flatshape. In its martensitic condition at T₁, the strip can be easilydeformed into a first bent shape. However, when the strip is heated soas to be in its austenitic condition at T₂, the strip attempts tostraighten out into the memorized flat shape.

Separable path 106 performs an additional function of heating breakermeans 108 from first temperature T₁ to second temperature T₂ whencurrent above the threshold value flows through separable path 106. As aresult, breaker means 108, if unrestrained, changes shape from the morebent configuration to the less bent configuration.

To manufacture separable path 106, electrically conductive layer 123 canbe deposited on polyimide/polymer film 122, as shown in FIG. 12. Forinstance, separable path 106 can comprise a polyimide film 122 which is0.0005 to 0.001 inch (0.0127 to 0.0254 mm) thick and 0.05 inch (1.27 mm)wide with a nichrome or copper layer 123 thereon in a thickness toprovide a desired resistance such as 1 ohm. However, various materialsand dimensions (length, width, thickness) can be utilized in designingseparable path 106.

Separable path 106 can be used with or without one or more electricallyinsulating coatings. However, to prevent leakage of current tosurrounding electrically conducting materials, path 106 can be providedwith a coating of dielectric material. For instance, separable path 106can include layer 125 of dielectric material on conductive layer 123, asshown in FIG. 14. The dielectric material can comprise any suitableelectrically insulating material such as polymer or ceramic materials.

The dielectric material 125 can be applied in any suitable manner suchas by techniques conventionally used in semiconductor processing. Forexample, a sheet of polyimide film 122 having a metallic layer ofnichrome or copper 123 can be masked off, and dielectric layer 125 canbe deposited on the polyimide film 122 in a desirable pattern.Alternatively, the conductive layer 123 can be etched to provide thedesired pattern on the polyimide film 122. The article shown in FIG. 15comprises a ribbon cut from such a sheet of polyimide film 122 havingconductive layer 123 and dielectric layer 125 thereon. Separable path106 can comprise a single strip cut from the ribbon shown in FIG. 15.

Separable path 106 can be used with or without contact pads. However, toprovide for optimized current flow into and out of path 106, pads 124 ofan electrically conducting corrosion resistant material can be providedon conductive layer 123. For instance, pads 124 can comprise a layeredstructure of copper, nickel, gold, etc. Pads 124 could also comprise asingle layer of copper, with tin-lead solder plating over the copperlayer.

To form pads 124, the metal or metals of the pad can be plated onconductive layer 123, as shown in FIG. 13. For instance, if dielectriclayer 125 is already present, the metal or metals of pads 124 can beplated directly on conductive layer 123.

As shown in FIG. 8, breaker means 108 is located on one side of path106. Dielectric layer 125 on separable path 106 faces and/or contactsbreaker means 108 and prevents flow of electrical current from separablepath 106 to breaker means 108 while allowing breaker means 108 to beheated to second temperature T₂ by heat produced by conductive layer 123when current above a threshold value I_(c) flows through separable path106. Path 106 can be used with or without adhesive means thereon.However, to provide for attachment to other parts, path 106 can includeadhesive layer 126. For instance, polymer film 122 can include adhesivelayer 126 on one side and conductive layer 123 on the other sidethereof, as shown in FIG. 14. Additional adhesive layers could beprovided on dielectric layer 125, if desired.

As shown in FIGS. 8 and 9, contacts 104,105 are immovable and havecontact zones located in interior space 113 within housing 102.Separable path 106 has contact zones 111,112 which are movable from afirst position (as shown in FIG. 8) in electrical contact with contactzones of contacts 104,105 to a second position (as shown in FIG. 9) outof electrical contact therewith. Contact zones 111,112 are in the firstposition when breaker means 108 is at the first temperature T₁, andcontact zones 111,112 are in the second position when breaker means 108is at the second temperature T₂.

Spring 107 normally urges contact zones 111, 112 into contact withcontacts 104,105. In particular, spring 107 comprises an elastic striphaving an arcuate central portion and ring-shaped end sections extendinginwardly from the central portion. Contact zones 111,112 of separablepath 106 are attached, such as by adhesive 126, to the respective endsections of spring 107. Spring 107 thus provides a force which biasescontact zones 111,112 of separable path 106 toward the contact zones ofcontacts 104,105 so that separable path 106 is in electrical contactwith contacts 104,105 when U-shaped breaker means 108 is at the firsttemperature T₁. U-shaped breaker means 108 provides a force which tendsto bend the end sections of spring 107 outwardly away from the contactzones of contacts 104,105 when U-shaped breaker means 108 is heated fromthe first temperature T, to the second temperature T₂, i.e., whenbreaker means 108 undergoes a metallurgical phase change and attempts torevert to a memorized shape. As a result, the gripping force acting oncontact zones 111,112 is relieved enough to allow tube spring 109 toovercome the force of spring 107, i.e., tube spring 109 slides contactzones 111,112 rectilinearly until they are out of contact with contacts104,105, as shown in FIG. 8.

Base 103 includes first, second and third support surfaces 120, 121 and114 within interior space 113. Contact zone 111 of first contact 104 isattached to first support surface 120. Contact zone 112 of secondcontact 105 is attached to second support surface 121. Tube spring 109is supported on third support surface 114. First and second supportsurfaces 120,121 comprise opposite sides of a vertical wall whichextends from base 103 into the center of interior space 113. Surface 114comprises an upper surface of an enlargement on top of the verticalwall. Contacts 104,105 can comprise copper platings on base 103 or apatterned copper plating on a single strip of polymer film.Alternatively, contacts 104,105 can comprise separate polymer films witha metallic layer on one side thereof. The polymer film can includeadhesive to attach the film to surfaces 120,121.

Tube spring 109 is elastically deformed in the non-circular shape shownin FIG. 9 when separable path 106 is in electrical contact with contacts104,105. However, when breaker means 108 is heated to the secondtemperature T₂, it provides enough of a counter force against the actionof spring 107 to weaken the grip of contact zones 111,112 on contacts104,105 and allow tube spring 109 to change to a circular shape, asshown in FIG. 8. Thus, the assembly of path 106, spring 107 and breakermeans 108 is pushed by contact with the inside surface 115 of breakermeans 108 by tube spring 109 toward the top of housing 102 and resultsin a wiping action of contact zones 111,112 on contacts 104,105.

Over-current/over-temperature protection device 100 includes a manuallyresettable mechanism. In particular, movable button 110 extends throughan upper part of housing 102 and includes a portion inside housing 102for pushing spring 107 and shape memory alloy breaker means 108 backinto a position at which separable path 106 is in contact with thecontact zones of contacts 104,105. When breaker means 108 is in itsmartensitic state at the first temperature T₁, the force of spring 107overcomes the force of breaker means 108, and contact zones 111,112 ofseparable path 106 stay in electrical contact with contact zones ofcontacts 104,105. When an over-current/over-temperature condition exits,tube spring 109 is able to overcome the force of spring 107 sincebreaker means 108 changes to its austenitic state and attempts to returnto the memorized shape thereby weakening the force of spring 107. As aresult, contact zones 111,112 slide along contacts 104,105 until theseparable path 106 is no longer in electrical contact with contacts104,105. Once the over-current/over-temperature condition no longerexits, breaker means 108 will cool and transform to its martensiticcondition thereby allowing spring 107 to apply greater force againstopposite sides of the vertical wall. The device can then be reset bypushing down on button 110, thereby returning tube spring 109 to thenon-circular configuration shown in FIG. 9.

A fourth embodiment of the over-current/over-temperature protectiondevice of the invention is shown in FIGS. 10 and 11. In particular,device 116 is similar to device 100 except that it includes remotelycontrolled resettable means. With respect to other features, like partsare identified with the same numerals as are used in FIGS. 8 and 9.

In the embodiment shown in FIGS. 10 and 11, breaker means 108 changesfrom a first bent configuration in its martensitic state to a secondless bent configuration in its austenitic state when heated from thefirst temperature T₁ to the second temperature T₂. As a result, spring107 is expanded such that contact zones 111,112 move out of contact withcontacts 104,105. When breaker means 108 cools sufficiently to transformto its martensitic state, the force of spring 107 bends breaker means108 until contact zones 111,112 are brought back into contact withcontacts 104,105, as in the second embodiment of the invention.

Remotely controlled device 116 includes control circuit path 117 whichis electrically insulated from contacts 104,105 and extends over surface118 on top of vertical wall 119 extending upwardly from base 103, asshown in the exploded view in FIG. 11. Surface 118 is complementary tothe concave surface of breaker means 108. When current above thethreshold value I_(c) is supplied from a remote source to control path117, control path 117 heats breaker means 108 to the second temperatureT₂. As a result, breaker means 108 transforms to its austenitic state ina remotely controlled manner. Breaker means 108 can also be heated totemperature T₂ by an over-temperature condition or an over-currentpassing through separable path 106.

As shown in FIGS. 16 and 17, control path 117 and contacts 104,105 canbe provided on a polymer film 127 by the technique described earlier formaking paths 4, 5 and 106. For instance, electrically conductive layer128 such as copper can be deposited on polymer film 127, and layer 128can be etched in a desirable pattern such as the pattern of electricallyconductive layer 128 shown in FIG. 16. Then dielectric layer 129 can beprovided on a central portion of the layer 128 corresponding to controlpath 117 to electrically insulate control path 117 from breaker means108. That is, dielectric layer 129 will be located between control path117 and the concave surface of breaker means 108. Dielectric layer 129should also cover enough of control path 117 to prevent electricalcontact between contact zones 111,112 and control path 117. Tocompensate for the increased height on layer 128 added by dielectriclayer 129, contacts 104,105 can be made thicker by building upelectrically conductive layers 130 on layers 128 so that separable path106 makes good electrical contact with contacts 104,105. For attachmentpurposes, the composite shown in FIGS. 16 and 17 can be provided withadhesive layer 131. That is, adhesive layer 131 can be used to securethe composite (104, 105, 117) to base 103 such that control path 117extends over surfaces 120, 118 and 121.

While the invention has been described with reference to the foregoingembodiments, various changes and modifications can be made to theinvention which fall within the scope of the appended claims.

What is claimed is:
 1. An over-current/over-temperature protectiondevice, comprising:first and second electrical contacts; a separableresistance electrical current path forming an electrical connectionbetween the contacts, the separable path having a resistance to flow ofelectrical current therethrough, the separable path comprising anelectrically conductive layer on a polymer film; breaker means forpreventing flow of electrical current between the contacts through theseparable path when current above a threshold value flows through theseparable path and/or the over-current/over-temperature protectiondevice reaches a threshold temperature, the means comprising a member ofa shape memory alloy which undergoes a metallurgical phase change whenheated from a first temperature T₁ to a second temperature T₂, themember when unrestrained being capable of changing from a firstconfiguration into a second configuration when heated from the firsttemperature T₁ to the second temperature T₂, the separable path beingseparated from at least one of the contacts when the member is heated tothe second temperature T₂ ; heater means for heating the member from thefirst temperature T₁ to the second temperature T₂, the heater meanscomprising the separable path; and resettable means for reconnecting theelectrical connection between the separable path and at least onecontact after the breaker means causes the electrical connection betweenthe separable path and the contacts to be broken.
 2. Theover-current/over-temperature protection device of claim 1, wherein theseparable path further comprises a layer of dielectric material on theconductive layer, the dielectric material preventing flow of electricalcurrent from the separable path to the member, the dielectric materialalso conducting heat to the member, the heat being produced by theconductive layer when current flows through the separable path.
 3. Anover-current/over-temperature protection device, comprising:first andsecond electrical contacts; a separable resistance electrical currentpath forming an electrical connection between the contacts, theseparable path having a resistance to flow of electrical currenttherethrough; breaker means for preventing flow of electrical currentbetween the contacts through the separable path when current above athreshold value flows through the separable path and/or theover-current/over-temperature protection device reaches a thresholdtemperature, the means comprising a member of a shape memory alloy whichundergoes a metallurgical phase change when heated from a firsttemperature T₁ to a second temperature T₂, the member when unrestrainedbeing capable of changing from a first configuration into a secondconfiguration when heated from the first temperature T₁ to the secondtemperature T₂, the separable path being separated from at least one ofthe contacts when the member is heated to the second temperature T₂ ;heater means for heating the member from the first temperature T₁ to thesecond temperature T₂, the heater means comprising the separable path;resettable means for reconnecting the electrical connection between theseparable path and at least one contact after the breaker means causesthe electrical connection between the separable path and the contacts tobe broken; and the contacts being immovable with respect to each other,the separable path having contact zones which are movable from a firstposition in electrical contact with the contacts to a second positionout of electrical contact with the contacts, the contact zones being inthe first position when the member is at the first temperature T₁ andthe contact zones being in the second position when the member is at thesecond temperature T₂.
 4. The over-current/over-temperature protectiondevice of claim 3, wherein the member is U-shaped, the contacts beinglocated between free ends of the U-shaped member, the ends of theU-shaped member being urged apart when the U-shaped member is at thesecond temperature T₂.
 5. The over-current/over-temperature protectiondevice of claim 3, further comprising spring means for biasing themember so as to be U-shaped when the member is at the first temperatureT₁ when the member is at the second temperature T₂.
 6. Theover-current/over-temperature protection device of claim 1, wherein theresettable means comprises a manually movable push button.
 7. Theover-current/over-temperature protection device of claim 6, wherein thepush button moves rectilinearly to slide the separable path from asecond position wherein the electrical connection is broken to a firstposition wherein the electrical connection is reconnected.
 8. Anover-current/over-temperature protection device, comprising:first andsecond electrical contacts; a separable resistance electrical currentpath forming an electrical connection between the contacts, theseparable path having a resistance to flow of electrical currenttherethrough; breaker means for preventing flow of electrical currentbetween the contacts through the separable path when current above athreshold value flows through the separable path and/or theover-current/over-temperature protection device reaches a thresholdtemperature, the means comprising a member of a shape memory alloy whichundergoes a metallurgical phase change when heated from a firsttemperature T₁ to a second temperature T₂, the member when unrestrainedbeing capable of changing from a first configuration into a secondconfiguration when heated from the first temperature T₁ to the secondtemperature T₂, the separable path being separated from at least one ofthe contacts when the member is heated to the second temperature T₂ ;heater means for heating the member from the first temperature T₁ to thesecond temperature T₂, the heater means comprising the separable path;resettable means for reconnecting the electrical connection between theseparable path and at least one contact after the breaker means causesthe electrical connection between the separable path and the contacts tobe broken; and arc minimizing means for minimizing arcing when theelectrical connection between at least one of the contacts and theseparable path is broken by the breaker means, the arc minimizing meanscomprising wiping means for sliding the separable path against at leastone of the contacts when the separable path is broken by the breakermeans.
 9. The over-current/over-temperature protection device of claim8, wherein the wiping means slides at least one of the contacts againstthe separable path when the separable path is electrically reconnectedto the contacts by the resettable means.
 10. Theover-current/over-temperature protection device of claim 5, furthercomprising a housing, the contacts being fixedly mounted in an interiorspace within the housing, the spring means comprising a strip of springmaterial having an arcuate central portion and end sections extendingfrom the central portion, each of the contact zones of the separablepath being attached to a respective one of the end sections, the springbiasing the contact zones of the separable path toward the contacts, theends of the U-shaped member urging the end sections of the spring meansapart with greater force when the U-shaped member is at the secondtemperature T₂ than when the U-shaped member is at the first temperatureT₁.
 11. The over-current/over-temperature protection device of claim 10,further comprising tube spring means for moving the separable path fromthe first position when the U-shaped member is at the first temperatureT₁ to the second position when the U-shaped member is at the secondtemperature T₂, the tube spring means comprising a tube spring which canbe elastically deformed from a circular configuration into anon-circular configuration, the tube spring being deformable into anon-circular configuration when the U-shaped member is at the firsttemperature T₁ and the tube spring elastically returning to the circularconfiguration when the member is heated from the first temperature T₁ tothe second temperature T₂, the tube spring being located in the interiorof the housing between a support surface and a concave surface of theU-shaped member.
 12. The over-current/over-temperature protection deviceof claim 11, wherein the U-shaped member is in a martensitic state whenthe U-shaped member is at the first temperature T₁ and the U-shapedmember is in an austenitic state when the U-shaped member is at thesecond temperature T₂.
 13. The over-current/over-temperature protectiondevice of claim 9, wherein the wiping means comprises a tube springwhich can be elastically deformed from a circular configuration into anon-circular configuration, the tube spring being deformable into thenon-circular configuration when the member is at the first temperatureT₁ and the tube spring elastically returning to the circularconfiguration when the member is heated from the first temperature T₁ tothe second temperature T₂.
 14. The over-current/over-temperatureprotection device of claim 12, wherein the resettable means comprises apush button having a first portion located outside the housing and asecond portion located inside the housing, the second portion moving theU-shaped member toward the tube spring so as to elastically deform thetube spring into the non-circular configuration when the first portionis moved toward the interior of the housing.
 15. Theover-current/over-temperature protection device of claim 1, wherein theresettable means comprises a second heater means for heating the memberfrom the first temperature T₁ to the second temperature T₂, the secondheater means comprising a control current path, the member being heatedto the second temperature when current above a threshold value passesthrough the control current path.
 16. The over-current/over-temperatureprotection device of claim 15, wherein the member changes shape from thefirst configuration to the second configuration when the member isheated from the first temperature T₁ to the second temperature T₂. 17.The over-current/over-temperature protection device of claim 16, whereinthe member is U-shaped and the ends of the U-shaped member are locatedcloser together in the first configuration than in the secondconfiguration, the device further comprising a support surface facing aconcave surface of the U-shaped member, the control current path beingsupported on the support surface.
 18. The over-current/over-temperatureprotection device of claim 17, wherein the contacts are fixedly mountedon a base, the separable path having contact zones which are movablefrom a first position in electrical contact with the contacts to asecond position out of electrical contact with the contacts, the contactzones being in the first position when the U-shaped member is in thefirst configuration and the contact zones being in the second positionwhen the U-shaped member is in the second configuration, the devicefurther comprising spring means for bending the U-shaped member in thefirst configuration when the U-shaped member is at the first temperatureT₁, the spring means also biasing the contact zones of the separablepath in the first position.
 19. The over-current/over-temperatureprotection device of claim 16, wherein the control current path iseffective for heating the member independently of the heater means, thecontrol current path being effective to change the member from the firstconfiguration to the second configuration by passing current above thethreshold value through the control current path and changing the memberback into the first configuration by interrupting the flow of currentthrough the control current path.